This invention relates generally to gas turbine engine combustors and more particularly to a fuel nozzle guide for use in such a combustor.
Gas turbine engine combustors include combustion chambers wherein compressed air is mixed with fuel sprayed into the combustion chamber by a fuel nozzle which extends into the combustion chamber through a hole in the chamber bulkhead. The air-fuel mixture is burned thereby increasing the kinetic energy of the resulting gases through the engine to produce useful power for the engine turbine and thrust for the engine.
Typically, a multicomponent fuel nozzle guide for receiving a fuel nozzle extends through an aperture in the chamber bulkhead to maintain the fuel nozzle and nozzle guide in proper alignment with the various other combustion chamber components such as the igniter plug and various air inlet apertures. The nozzle guide also aids in the insertion of the nozzle for combustor assembly and maintenance. Such a nozzle guide usually includes various air apertures for cooling and mixing. The environment within a gas turbine engine is extremely harsh. The air-fuel mixture burns in the combustion chamber at temperatures as high as 2100xc2x0 C. causing extreme thermal gradients and thermal stresses in the chamber walls. The nozzle guide typically moves with the nozzle and slides with respect to the bulkhead to accommodate thermal growth of the components which might occur at different rates for the components.
In prior nozzle guides such as disclosed in Butler et al., U.S. Pat. No. 5,419,115 issued May 30, 1995 for Bulkhead and Fuel Nozzle Guide Assembly For An Annular Combustion Chamber, the nozzle guide comprises two components. In assembling the nozzle guide in the bulkhead aperture, one component is inserted from the upstream (or xe2x80x9ccoldxe2x80x9d) side of the bulkhead and the other component is inserted from the downstream (or xe2x80x9chotxe2x80x9d) side. The two components are then welded together. The nozzle is thereafter inserted in the nozzle guide from the upstream side. Any service or repair on the combustor which includes removal of the nozzle guide will require the cutting apart of the two nozzle guide components. Suliga, U.S. Pat. No. 4,870,818 issued Oct. 3, 1989 for Fuel Nozzle Guide Structure and Retainer For A Gas Turbine Engine discloses a similar nozzle guide configuration.
It would be desirable to provide a nozzle guide which is attached to the cold side of the bulkhead rather than the harsh, hot side environment. It would also be desirable to provide a nozzle guide that does not require the manufacturing step of welding the nozzle components together during assembly. Further, to facilitate disassembly of the nozzle guide, it would be desirable to eliminate the necessity of a cutting operation.
In addition to mounting the nozzle, the nozzle guide may contribute to fuel mixing in the combustion chamber in particular engine applications. Gas turbine engines emit various pollutants including oxides of nitrogen (xe2x80x9cNOxxe2x80x9d). NOx is primarily formed through the thermal fixation of nitrogen and results from the high temperature combustion of fuel and air in the gas turbine engine. Environmental concerns and more stringent governmental regulation of NOx emissions have prompted designers to pursue various methods for reducing the generation of NOx by gas turbine engines. Two basic approaches for a low NOx fuel injection system are (1) a locally lean stoichiometry system and (2) a locally rich stoichiometry system. Both approaches require good atomization, mixing and uniformity in the fuel-air mixture. It would be desirable to provide a nozzle guide that complements nozzles of the radial inflow design and that contributes to improved atomization, mixing and/or uniformity in low Nox applications.
It is an object of the present invention to provide a new and improved fuel nozzle guide which affords ease of assembly and disassembly relative to the combustor bulkhead.
Another object of the invention is to provide an integral, one-piece nozzle guide that is mountable to the combustor bulkhead from one side.
A further object of the invention is to provide a nozzle guide that is attached to the cold side of the combustor bulkhead.
Another object is to provide an alternate embodiment of nozzle guide that can provide swirling air to the fuel-air spray from the nozzle. Included within this objective is the provision of a design that may be used to mount a nozzle of the type having a radial inflow swirler.
A further object is to provide a new and improved method of assembling a nozzle guide to a combustor bulkhead and disassembling the nozzle guide therefrom.
Other objects will be in part apparent and in part pointed out more in detail hereinafter.
Accordingly, it has been found that the foregoing and related objects and advantages are attained in a fuel nozzle guide having a frusto-conical hub section forming a central mounting aperture to receive a fuel nozzle, an annular base, a radial inflow swirler, and a pair of retaining tabs extending from the base for mounting to the outer bulkhead wall of a combustor. In one embodiment each tab has an elongated aperture to mount a bushing secured to the bulkhead wall so as to allow limited movement relative to the bulkhead. In another embodiment, each tab is configured to be received in a slot formed at the bulkhead wall by a retainer secured to the bulkhead wall so as to allow limited movement relative to the bulkhead.
In the method of the present invention, the nozzle guide is inserted into the bulkhead mounting aperture from the cold side of the bulkhead and mechanically secured to the bulkhead wall so as to allow predetermined limited movement relative to the bulkhead to accommodate thermal expansion during operation and fuel nozzle installation. In the method of disassembly, the nozzle guide is mechanically disconnected from the cold side of the bulkhead and withdrawn from the bulkhead mounting aperture.